CN111355025A

CN111355025A - Dual-frequency circularly polarized antenna structure

Info

Publication number: CN111355025A
Application number: CN201911279670.0A
Authority: CN
Inventors: 吴建逸; 吴朝旭; 黄士耿; 吴正雄; 杨易儒; 柯庆祥; 许胜钦
Original assignee: Pegatron Corp
Current assignee: Pegatron Corp
Priority date: 2018-12-20
Filing date: 2019-12-13
Publication date: 2020-06-30
Anticipated expiration: 2039-12-13
Also published as: TWI674706B; TW202025552A; US20200203835A1; CN111355025B; US11056789B2

Abstract

The invention discloses a dual-frequency circularly polarized antenna structure which comprises a microstrip line, an antenna unit and a ground plane. The antenna unit comprises a first radiator and a second radiator. The first radiator is provided with a feed-in part and a first spiral part, and the starting point of the first spiral part surrounds outwards from the part close to the feed-in part. The second radiator has a first grounding part and a second spiral part corresponding to the feed-in part, the starting point of the second spiral part is not overlapped with the first spiral part from the part close to the first grounding part and surrounds outwards, and one of the first radiator and the second radiator is also provided with a second grounding part. The microstrip line and the antenna unit are arranged at intervals, and the feed-in part of the first radiator of the antenna unit is coupled to the microstrip line. The second grounding part and the first grounding part are coupled to the grounding surface. The dual-frequency circularly polarized antenna structure of the invention provides broadband dual-frequency bands and can enable the dual-frequency circularly polarized antenna structure to have smaller volume.

Description

Dual-frequency circularly polarized antenna structure

Technical Field

The present invention relates to an antenna structure, and more particularly, to a dual-band circularly polarized antenna structure.

Background

Currently, circular polarized antennas usually require a large volume of space, and it is not easy to design an antenna performance that has dual bands, wide frequency bands, and a good Axial Ratio (Axial Ratio). Therefore, how to design an antenna device having a small volume, having dual frequency bands, and having a good axial ratio is a big issue nowadays.

Disclosure of Invention

The invention provides a dual-frequency circularly polarized antenna structure which can provide broadband dual-frequency bands and has a small volume.

The invention relates to a dual-frequency circularly polarized antenna structure which comprises a microstrip line, an antenna unit and a ground plane. The antenna unit is disposed on a first substrate. The antenna unit comprises a first radiator and a second radiator. The first radiator is provided with a feed-in part and a first spiral part, and the starting point of the first spiral part surrounds outwards from the part close to the feed-in part. The second radiator has a first grounding part and a second spiral part corresponding to the feed-in part, the starting point of the second spiral part is not overlapped with the first spiral part from the part close to the first grounding part and surrounds outwards, and one of the first radiator and the second radiator is also provided with a second grounding part. The microstrip line is arranged on a second substrate which is arranged in parallel with the first substrate at a distance, and the feed-in part of the first radiator of the antenna unit is coupled to the microstrip line. The grounding surface is arranged on the second substrate, and the second grounding part and the first grounding part are coupled to the grounding surface.

In an exemplary embodiment of the invention, the antenna unit is disposed on an upper surface of the first substrate, the microstrip line is disposed on one of an upper surface and a lower surface of the second substrate, and the ground plane is disposed on the other of the upper surface and the lower surface of the second substrate, wherein the upper surface of the second substrate is adjacent to the first substrate compared to the lower surface.

In an exemplary embodiment of the invention, the microstrip line includes a first segment, a second segment, a third segment and a fourth segment from the center to the edge of the second substrate, the widths of the second segment and the fourth segment are greater than the widths of the first segment and the third segment, and the length of the second segment is between 3 mm and 4 mm.

In an exemplary embodiment of the invention, the first spiral portion and the second spiral portion respectively extend from a start point of the first spiral portion and a start point of the second spiral portion to a center to form two rectangles, the feeding portion and the first grounding portion are respectively located in the two rectangles, a connection line of the two rectangles is perpendicular to an extending direction of the microstrip line, and the first radiator has the second grounding portion.

In an exemplary embodiment of the invention, the first spiral portion and the second spiral portion respectively extend from a start point of the first spiral portion and a start point of the second spiral portion to a center to form two rectangles, the feeding portion and the first grounding portion are respectively located in the two rectangles, a connection line direction of the two rectangles is parallel to an extending direction of the microstrip line, and the second radiator has the second grounding portion.

In an exemplary embodiment of the invention, a width of each of the rectangles is between 1.5 mm and 2.5 mm, a length of each of the rectangles is between 3.5 mm and 5 mm, and a distance between the two rectangles is between 1.5 mm and 2.5 mm, wherein the width of the rectangle is perpendicular to a line connecting a starting point of the first spiral part and a starting point of the second spiral part, and the length of the rectangle is parallel to a line connecting the starting point of the first spiral part and the starting point of the second spiral part.

In an exemplary embodiment of the invention, a distance between a center of the first spiral portion and the second spiral portion and the feeding portion is between 2 mm and 3 mm, a distance between the center and the first grounding portion is between 2 mm and 3 mm, and a distance between the center and the second grounding portion is between 6 mm and 8 mm.

In an exemplary embodiment of the invention, the distance between the starting point of the first spiral part and the starting point of the second spiral part is 8.5 mm to 12.5 mm, and the diameter of each of the first spiral part and the second spiral part is 50 mm to 55 mm.

In an exemplary embodiment of the invention, the feeding portion, the first grounding portion and the second grounding portion are arranged in a straight line.

In an exemplary embodiment of the invention, the first radiator has the second ground portion, the second ground portion is located at a position where the second ground portion rotates 260 degrees from the feeding portion along the first radiator, the second radiator further has a third ground portion coupled to the ground plane, and the third ground portion is located at a position where the third ground portion rotates 180 degrees from the first ground portion along the second radiator.

In an exemplary embodiment of the invention, the microstrip line has a first section, a second section, a third section and a fourth section, widths of the second section and the fourth section are greater than widths of the first section and the third section, a length of the second section is between 7 mm and 9 mm, and a length of the third section is between 2 mm and 4 mm.

In an exemplary embodiment of the invention, a connection line of the feeding portion and the first grounding portion is perpendicular to an extending direction of the microstrip line.

In an exemplary embodiment of the invention, an angle between a connection line of the feeding portion and the first grounding portion and an extending direction of the microstrip line is 10 degrees to 20 degrees.

Based on the above, the antenna unit of the dual-band circularly polarized antenna structure of the present invention uses the first radiator and the second radiator as two starting points at the positions close to the feeding portion and the first grounding portion, respectively, and surrounds two spiral portions outwards, and the feeding portion is coupled to the microstrip line below the antenna unit, so that the dual-band circularly polarized antenna structure of the present invention can provide a broadband dual-band. In addition, the design can enable the dual-frequency circularly polarized antenna structure to have a smaller volume.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

Fig. 1 is a schematic diagram of a dual-band circularly polarized antenna structure according to an embodiment of the invention.

Fig. 2 is a side view schematic diagram of the dual-band circularly polarized antenna structure of fig. 1.

Fig. 3 is a schematic top view of a first substrate of the dual-band circularly polarized antenna structure of fig. 1.

Fig. 4 is a schematic top view of a second substrate of the dual-band circularly polarized antenna structure of fig. 1.

Fig. 5 is a schematic bottom view of a second substrate of the dual-band circularly polarized antenna structure of fig. 1.

Fig. 6 is a schematic diagram of a dual-band circularly polarized antenna structure according to another embodiment of the invention.

Fig. 7 is a schematic diagram of the frequency-to-voltage standing wave ratio of the dual-frequency circularly polarized antenna structure of fig. 1 and 6.

Fig. 8 is a schematic diagram of the frequency-antenna efficiency of the dual-band circularly polarized antenna structure of fig. 1 and 6.

Fig. 9 is a schematic diagram of the frequency-to-axial ratio of the dual-frequency circularly polarized antenna structure of fig. 1 and 6.

Fig. 10 is a schematic diagram of a dual-band circularly polarized antenna structure according to another embodiment of the invention.

Fig. 11 is a schematic top view of a first substrate of the dual-band circularly polarized antenna structure of fig. 10.

Fig. 12 is a schematic top view of a second substrate of the dual-band circularly polarized antenna structure of fig. 10.

Fig. 13 is a bottom view of the second substrate of the dual-band circularly polarized antenna structure of fig. 10.

Fig. 14 is a schematic diagram of the frequency-axial ratio pattern distribution of the dual-frequency circularly polarized antenna structure of fig. 10.

Figure 15 is a schematic diagram of the frequency-to-voltage standing wave ratio of the dual-frequency circularly polarized antenna structure of figure 10.

Fig. 16 is a schematic diagram of the frequency-antenna efficiency of the dual-band circularly polarized antenna structure of fig. 10.

Fig. 17A and 17B are E ψ and E θ field patterns of the XZ plane and the YZ plane of the dual-band circularly polarized antenna structure of fig. 10 at a frequency of 2450 MHz.

Fig. 17C and 17D are graphs of E ψ and E θ fields of the XZ plane and the YZ plane of the dual-band circularly polarized antenna structure of fig. 10 at a frequency of 5500 MHz.

Fig. 18 is a schematic diagram of a dual-band circularly polarized antenna structure according to another embodiment of the invention.

Fig. 19 is a schematic top view of a first substrate of the dual-band circularly polarized antenna structure of fig. 18.

Fig. 20 is a schematic diagram of the frequency-to-axial ratio pattern distribution of the dual-frequency circularly polarized antenna structure of fig. 18.

Description of reference numerals:

a 1: width of rectangle

a2, R2: distance between each other

R1: diameter of

a 3: length of

A to E: segment of

D1-D6, H, W: distance between two adjacent plates

T1, T2: thickness of

Phi-axis and theta-axis electric field components

θ 1, θ 2: angle of rotation

100. 100a, 100b, 100 c: dual-frequency circularly polarized antenna structure

110: first substrate

1101: upper surface of

1102: lower surface

111: antenna unit

112: first radiator

1121. 1121 b: first screw part

113: second radiator

1131. 1131 b: second screw part

114. 114a, 114b, 114 c: feed-in part

115. 117: rectangle

1151: starting point of the first spiral part

1171: starting point of the second spiral part

116. 116a, 116b, 116 c: first grounding part

118. 118b, 118 c: second grounding part

119. 119 c: third grounding part

120: second substrate

122: upper surface of

124: lower surface

125: ground plane

127: dead zone

130: microstrip line

140: the first conductive column

142. 144, 146: the second conductive column

150: spacer member

160: antenna signal connector

Detailed Description

Fig. 1 is a schematic diagram of a dual-band circularly polarized antenna structure according to an embodiment of the invention. Fig. 2 is a side view schematic diagram of the dual-band circularly polarized antenna structure of fig. 1. Fig. 3 is a schematic top view of a first substrate of the dual-band circularly polarized antenna structure of fig. 1. Fig. 4 is a schematic top view of a second substrate of the dual-band circularly polarized antenna structure of fig. 1. Fig. 5 is a schematic bottom view of a second substrate of the dual-band circularly polarized antenna structure of fig. 1.

Referring to fig. 1 to fig. 5, the dual-band circularly polarized antenna structure 100 of the present embodiment is a dual-band (e.g., WiFi2.4GHz at low frequency and WiFi 5GHz at high frequency) circularly polarized antenna. Of course, the range of the dual band is not limited to the above. The dual-band circularly polarized antenna structure 100 of the present embodiment includes a microstrip line 130 (fig. 2), an antenna unit 111 and a ground plane 125. As shown in fig. 2, the antenna unit 111 is disposed on one side of the microstrip line 130 and spaced apart from the microstrip line 130. The ground plane 125 is disposed on one side of the antenna unit 111 and spaced apart from the antenna unit 111.

As shown in fig. 3, in the present embodiment, the antenna unit 111 includes a first radiator 112 and a second radiator 113. The first radiator 112 has a feeding portion 114 and a first spiral portion 1121, and a starting point 1171 of the first spiral portion 1121 is surrounded from a portion close to the feeding portion 114. The second radiator 113 has a first grounding portion 116 corresponding to the position of the feeding portion 114 and a second spiral portion 1131, and a starting point 1151 of the second spiral portion 1131 does not overlap the first spiral portion 1121 to surround from a portion close to the first grounding portion 116. That is to say, the first radiator 112 and the second radiator 113 respectively surround the first spiral portion 1121 and the second spiral portion 1131 outwards with the portions close to the feeding portion 114 and the first grounding portion 116 as two

starting points

1151 and 1171, and one of the first radiator 112 and the second radiator 113 further has a second grounding portion 118.

In addition, as shown in fig. 2, in the present embodiment, the dual-band circularly polarized antenna structure 100 further includes a first substrate 110, a second substrate 120, a first conductive via 140, and two second

conductive vias

142 and 144. The antenna unit 111 is disposed on the upper surface 1101 of the first substrate 110. The second substrate 120 is disposed parallel to the first substrate 110 and spaced apart by a distance. In the present embodiment, the first substrate 110 and the second substrate 120 are separated by the spacer 150, so that a certain distance is maintained between the first substrate 110 and the second substrate 120. The spacer 150 is, for example, a plastic support or foam, but the type of the spacer 150 is not limited thereto.

In addition, the microstrip line 130 is disposed on one of the upper surface 122 and the lower surface 124 of the second substrate 120, and the ground plane 125 is disposed on the other of the upper surface 122 and the lower surface 124 of the second substrate 120. In the embodiment, the ground plane 125 is disposed on the upper surface 122 of the second substrate 120, the microstrip line 130 is disposed on the lower surface 124 of the second substrate 120, and the upper surface 122 of the second substrate 120 is adjacent to the first substrate 110 (as shown in fig. 2) compared to the lower surface 124, but the positions of the ground plane 125 and the microstrip line 130 are not limited thereto.

In the present embodiment, the feeding element 114 is coupled to the microstrip line 130. The second ground portion 118 and the first ground portion 116 are coupled to the ground plane 125. In detail, the first conductive via 140 is disposed between the first substrate 110 and the second substrate 120, and the feeding portion 114 is connected to the microstrip line 130 through the first conductive via 140. The two second

conductive vias

142, 144 are disposed between the first substrate 110 and the second substrate 120, and the second ground portion 118 and the first ground portion 116 are connected to the ground plane 125 through the two second

conductive vias

142, 144, respectively. In the embodiment, the first conductive via 140 and the second

conductive vias

142 and 144 are, for example, copper pillars, and the diameter is, for example, 1 mm, but the material and the size of the first conductive via 140 and the second

conductive vias

142 and 144 are not limited thereto.

As shown in fig. 2, in the present embodiment, the thickness T1 of the antenna element 111 and the first substrate 110 is generally between 0.6 mm and 1 mm (e.g., 0.8 mm), the thickness T2 of the ground plane 125, the microstrip line 130 and the second substrate 120 is generally between 1.2 mm and 2 mm (e.g., 1.6 mm), and the distance H between the antenna element 111 on the upper surface 1101 of the first substrate 110 and the ground plane 125 or microstrip line 130 on the lower surface 124 of the second substrate 120 is 1/4 and is generally between 18 mm and 21 mm (e.g., 19.4 mm). Of course, the above dimensions are not limited thereto.

In the present embodiment, the distance between the lower surface 1102 of the first substrate 110 and the upper surface 122 of the second substrate 120 is 1/4 wavelengths (about 17 mm) of a high frequency signal (e.g., 5GHz) generated by the antenna structure 100. In practical applications, the distance between the lower surface 1102 of the first substrate 110 and the upper surface 122 of the second substrate 120 is adjusted so that the antenna structure 100 can perform well at both the Axial Ratio of low frequency (Axial Ratio) and high frequency (Axial Ratio), which is set to 17 mm, for example. Of course, the above dimensions are not limited thereto.

As shown in fig. 3, in the present embodiment, the first spiral portion 1121 and the second spiral portion 1131 of the antenna unit 111 extend from two

start points

1151, 1171 to a center to form two

rectangles

115, 117, and the feeding portion 114 and the first grounding portion 116 are respectively located in the two

rectangles

115, 117. In the present embodiment, the second ground portion 118 is formed on the first radiator 112 as an example. In the present embodiment, the second grounding portion 118 is located at a position rotated 180 degrees from the feeding portion 114 along the first radiator 112, so that the first grounding portion 116 is located between the feeding portion 114 and the second grounding portion 118, and the feeding portion 114, the first grounding portion 116 and the second grounding portion 118 are arranged in a straight line. Of course, the positions of the feeding portion 114, the first grounding portion 116 and the second grounding portion 118 are not limited thereto.

In the present embodiment, the width a1 of each

rectangle

115, 117 is perpendicular to the line connecting the two

starting points

1151, 1171 of the first spiral portion 1121 and the second spiral portion 1131, and the length a3 of each

rectangle

115, 117 is parallel to the line connecting the two

starting points

1151, 1171 of the first spiral portion 1121 and the second spiral portion 1131. The width a1 of each

rectangle

115, 117 is between 1.5 mm and 2.5 mm (e.g., 2 mm), the length a3 of each

rectangle

115, 117 is between 3.5 mm and 5 mm (e.g., 4 mm), and the distance a2 between the two

rectangles

115, 117 is between 1.5 mm and 2.5 mm (e.g., 2 mm). In the present embodiment, the width a1 and the length a3 of the

rectangles

115 and 117 or the distance a2 between the two

rectangles

115 and 117 are changed to adjust the antenna frequency and impedance matching of the dual-band circularly polarized antenna structure 100 at low and high frequencies.

In addition, as shown in fig. 3, in the present embodiment, a distance D1 between a center of the first spiral portion 1121 and the second spiral portion 1131 and the feeding portion 114 is between 2 mm and 3 mm (for example, 2.5 mm), a distance D2 between the center of the first spiral portion 1121 and the second spiral portion 1131 and the first grounding portion 116 is between 2 mm and 3 mm (for example, 2.5 mm), and a distance D3 between the center of the first spiral portion 1121 and the second spiral portion 1131 and the second grounding portion 118 is between 6 mm and 8 mm (for example, 7 mm).

In addition, in the present embodiment, the distance R2 between the two

starting points

1151 and 1171 of the first spiral portion 1121 and the second spiral portion 1131 is between 8.5 mm and 12.5 mm (for example, 10.5 mm), and the diameter (i.e., the distance between the two end points) R1 of each of the first spiral portion 1121 and the second spiral portion 1131 is between 50 mm and 55 mm (for example, 52.5 mm). The diameter R1 may determine the resonant frequency of the antenna structure 100 at low frequencies and the spacing R2 may determine the resonant frequency of the antenna structure 100 at high frequencies. Of course, the above dimensions are not limited thereto.

Referring to fig. 2 and fig. 4, in the present embodiment, the ground plane 125 is located between the antenna unit 111 and the microstrip line 130, the ground plane 125 has a vacant area 127, and the ground plane 125 may be fully distributed on the upper surface 122 of the second substrate 120 except for the vacant area 127. The first conductive via 140 penetrates the second substrate 120, and the portion of the first conductive via 140 on the upper surface 122 of the second substrate 120 is located in the empty region 127 and is not conductive to the ground plane 125. In the present embodiment, the minimum distance W between the first conductive via 140 and the edge of the empty area 127 is between 0.5 mm and 1.5 mm (e.g., 1 mm). The minimum distance W between the first conductive via 140 and the edge of the empty area 127 is sized to improve impedance matching of the high frequency of the dual-band circularly polarized antenna structure 100.

In addition, referring to fig. 5, in the present embodiment, the dual-band circularly polarized antenna structure 100 further includes an antenna signal connector 160 disposed at the edge of the second substrate 120. One end a of the microstrip line 130 is connected to the first conductive via 140, and the other end C of the microstrip line 130 is connected to the antenna signal connector 160. The feeding portion 114 of the antenna unit 111 is connected to a signal positive terminal of an antenna signal connector 160 (e.g., an SMA connector) through the first conductive via 140 and the microstrip line 130, and the first ground portion 116 and the second ground portion 118 of the antenna unit 111 are connected to a signal negative terminal of the antenna signal connector 160 through the second

conductive vias

142 and 144 and the ground plane 125, respectively.

In addition, as shown in fig. 5, the microstrip line 130 divides a first section (AD section), a second section (DE section), a third section (EB section) and a fourth section (BC section) from the first conductive via 140 to the antenna signal connector 160, the widths of the second section (DE section) and the fourth section (BC section) are greater than the widths of the first section (AD section) and the third section (EB section), and the length D4 of the second section (DE section) is between 3 mm and 4 mm (e.g., 3.5 mm), so as to achieve better impedance matching.

In the present embodiment, a Radio Frequency (RF) transmission signal enters the microstrip line 130 through the antenna signal connector 160, and the size of the microstrip line 130 in the fourth section (BC section) is calculated by a path of 1/4 wavelength of high Frequency, and is about 15 mm, where the BC section is 3 mm wide.

In this embodiment, the length of the AB segment is 1/4 wavelength path for high frequency, i.e. 15 mm, as calculated by the impedance matching transformation formula, wherein the width of the AB segment is 0.7 mm. In the present embodiment, a rectangle with a length and a width of 3.5 mm and 3 mm is disposed in the center of the AB segment of the microstrip line 130, i.e., between the first segment (AD segment) and the third segment (EB segment), as the second segment (DE segment), for adjusting the impedance matching of the antenna band of the dual-band circularly polarized antenna structure 100.

In the present embodiment, the dual-band circularly polarized antenna structure 100 utilizes the first radiator 112 and the second radiator 113 to surround the first spiral portion 1121 and the second spiral portion 1131, respectively, and combines with the feeding structure of the microstrip line 130, so as to form a small dual-band (WiFi 2.4GHz and WiFi 5GHz) circularly polarized antenna. The overall volume of the dual-band circularly polarized antenna structure 100 may be a combination of 60 mm, 60 mm and 19.4 mm in length, width and height, and is suitable for being applied to a factory test terminal or a research and development terminal to be used as a test fixture for testing a product to be tested due to its small volume. The dual-band circularly polarized antenna structure 100 can be applied to near-field wireless performance test at a factory RF end, and can simultaneously have transmitting or receiving intensity in a Co-plane Polarization (Co-Polarization) direction and a Cross Polarization (Cross-Polarization) direction for a product to be tested.

The following describes other embodiments of the dual-band circularly polarized antenna structure, and the same or similar elements as those in the previous embodiment are denoted by the same or similar symbols, and are not further described. Only the main differences will be explained below.

Fig. 6 is a schematic diagram of a dual-band circularly polarized antenna structure according to another embodiment of the invention. Referring to fig. 6, a difference between the dual-band circularly polarized antenna structure 100a of fig. 6 and the dual-band circularly polarized antenna structure 100 of fig. 1 is that in fig. 1, the second grounding portion 118 is formed on the first radiator 112, so that the first grounding portion 116 is located between the feeding portion 114 and the second grounding portion 118, and a connection direction between the feeding portion 114 and the first grounding portion 116 is perpendicular to an extending direction of the microstrip line 130. In contrast, in the present embodiment, the second grounding portion 118 is formed on the second radiator 113, so that the feeding portion 114a is located between the first grounding portion 116a and the second grounding portion 118, and the connection line direction of the feeding portion 114a and the first grounding portion 116a is parallel to the extending direction of the microstrip line 130.

Fig. 7 is a schematic diagram of the frequency-to-voltage standing wave ratio of the dual-frequency circularly polarized antenna structure of fig. 1 and 6. Referring to fig. 7, the dual-band circularly polarized antenna structure 100 of fig. 1 and the dual-band circularly polarized antenna structure 100a of fig. 6 have a VSWR of less than 3 in the low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz) bands, respectively, and thus have good performance.

Fig. 8 is a schematic diagram of the frequency-antenna efficiency of the dual-band circularly polarized antenna structure of fig. 1 and 6. Referring to fig. 8, the dual-band circularly polarized antenna structure 100 of fig. 1 and the dual-band circularly polarized antenna structure 100a of fig. 6 have good performance in both low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz) bands, with antenna efficiency greater than-3 dBi, even greater than-2.5 dBi.

Fig. 9 is a schematic diagram of the frequency-to-axial ratio of the dual-frequency circularly polarized antenna structure of fig. 1 and 6. Referring to fig. 9, the axial ratio of the dual-band circularly polarized antenna structure 100 of fig. 1 and the dual-band circularly polarized antenna structure 100a of fig. 6 is substantially less than 3dB in the low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz), and particularly, the axial ratio of the dual-band circularly polarized antenna structure 100 of fig. 6 is less than 3dB, so that the performance is good.

Fig. 10 is a schematic diagram of a dual-band circularly polarized antenna structure according to another embodiment of the invention. Fig. 11 is a schematic top view of a first substrate of the dual-band circularly polarized antenna structure of fig. 10. Fig. 12 is a schematic top view of a second substrate of the dual-band circularly polarized antenna structure of fig. 10. Fig. 13 is a bottom view of the second substrate of the dual-band circularly polarized antenna structure of fig. 10.

Referring to fig. 10 to 13, in the present embodiment, the microstrip line 130b of the dual-band circularly polarized antenna structure 100b is located between the antenna unit 111b and the ground plane 125 (fig. 13). That is, in the present embodiment, the microstrip line 130b is located on the upper surface 122 of the second substrate 120 (fig. 12), and the ground plane 125 is located on the lower surface 124 of the second substrate 120 (fig. 12). In this embodiment, since the microstrip line 130b and the antenna unit 111b are both disposed above the ground plane 125, the radiation energy of the antenna can be concentrated, and the radiation of the back energy below the ground plane 125 can be reduced.

In addition, as can be seen from fig. 11, in the present embodiment, the second ground portion 118b is located at a position rotated by 260 degrees along the first radiator 112b from the feeding portion 114 b. In the present embodiment, the second radiator 113b further has a third grounding portion 119, the third grounding portion 119 is coupled to the ground plane 125 through the second conductive via 146, and the third grounding portion 119 is located at a position rotated 180 degrees along the second radiator 113 from the first grounding portion 116 b. In the present embodiment, the feeding portion 114b, the first grounding portion 116b, the second grounding portion 118b and the third grounding portion 119 are configured to enable the dual-band circularly polarized antenna structure 100 to have a better axial ratio.

In the present embodiment, the shapes of the first spiral portion 1121b and the second spiral portion 1131b of the antenna unit 111b near the center point are close to the circular shape (i.e., the sector shape) of 1/4, and the feeding portion 114b and the first ground portion 116b are respectively located in the circular shapes of the two portions 1/4. Of course, the shapes of the first spiral portion 1121b and the second spiral portion 1131b of the antenna unit 111b near the center point are not limited thereto.

Further, as shown in fig. 12, in the present embodiment, the length D5 of the second section (DE section) of the microstrip line 130b is between 7 mm and 9 mm (for example, 8 mm), and the width thereof is about 3 mm. The length D6 of the third section (EB section) is between 2 mm and 4 mm (e.g., 3 mm). Such dimensions can improve the axial ratio characteristics in the YZ plane at high frequencies, and improve the antenna efficiency of the dual-band circularly polarized antenna structure 100b at high frequencies.

Fig. 14 is a schematic diagram of the frequency-axial ratio pattern distribution of the dual-frequency circularly polarized antenna structure of fig. 10. Note that, in fig. 14, only the region where the axial ratio is less than 3dB is shown, and the dotted region represents the region where the axial ratio is less than 3 dB. Referring to fig. 14, the dual-band circularly polarized antenna structure 100b of the present embodiment has a good performance in the low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz) bands, and the axial ratio of the XZ plane to the YZ plane is less than 3dB at a position where θ is 0 (i.e., in the Z direction, right above the dual-band circularly polarized antenna structure 100 b).

Figure 15 is a schematic diagram of the frequency-to-voltage standing wave ratio of the dual-frequency circularly polarized antenna structure of figure 10. Referring to fig. 15, the dual-band circularly polarized antenna structure 100b of the present embodiment has a VSWR of less than 3 in the low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz) bands, and thus has good performance.

Fig. 16 is a schematic diagram of the frequency-antenna efficiency of the dual-band circularly polarized antenna structure of fig. 10. Referring to fig. 16, the dual-band circularly polarized antenna structure 100b of the present embodiment has good performance in both low-frequency (i.e., 2.4GHz) and high-frequency (i.e., 5GHz) bands, with the antenna efficiency being greater than-3 dBi, even greater than-2 dBi.

Fig. 17A and 17B are graphs of Phi-axis electric field components E ψ and theta-axis electric field components E θ of the XZ plane (Phi is 0) and the YZ plane (Phi is 90) of the dual-band circularly polarized antenna structure of fig. 10 at a frequency of 2450 MHz. Fig. 17C and 17D are graphs of E ψ and E θ fields of the XZ plane and the YZ plane of the dual-band circularly polarized antenna structure of fig. 10 at a frequency of 5500 MHz. Referring to fig. 17A to 17D, in the dual-band circularly polarized antenna structure 100b of the present embodiment, at the frequency bands of low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz), E ψ and E θ are places where the maximum energy is at an angle of 0, and E ψ and E θ overlap within 3dB at an angle of 0, that is, the XZ plane and the YZ plane have circular polarization characteristics, and can transmit or receive signals simultaneously.

Fig. 18 is a schematic diagram of a dual-band circularly polarized antenna structure according to another embodiment of the invention. Fig. 19 is a schematic top view of a first substrate of the dual-band circularly polarized antenna structure of fig. 18. Referring to fig. 18 and 19, a main difference between the dual-band circularly polarized antenna structure 100c of fig. 18 and the dual-band circularly polarized antenna structure 100b of fig. 10 is that in fig. 10, a connection line between the feeding portion 114b and the first grounding portion 116b is perpendicular to an extending direction of the microstrip line 130 b. If the dual-band circularly polarized antenna structure 100b of fig. 10 is rotated by an angle θ 1 (shown in fig. 19) of the entire antenna unit 111b around the feeding portion 114b, where θ 1 is between 70 degrees and 80 degrees, for example, 75 degrees, the dual-band circularly polarized antenna structure 100c of fig. 18 is obtained.

In the present embodiment, an angle θ 2 (shown in fig. 19) between a connection line of the feeding portion 114c and the first grounding portion 116c and the extending direction of the microstrip line 130b is between 10 degrees and 20 degrees (for example, 15 degrees), so as to improve the axial ratio characteristic of the high frequency of the dual-band circularly polarized antenna structure 100c in the XZ plane and the YZ plane.

Fig. 20 is a schematic diagram of the frequency-to-axial ratio pattern distribution of the dual-frequency circularly polarized antenna structure of fig. 18. Note that, in fig. 20, only the region where the axial ratio is less than 3dB is shown, and the dotted region represents the region where the axial ratio is less than 3 dB. Referring to fig. 20, the dual-band circularly polarized antenna structure 100c of the present embodiment has a good performance in the low frequency (i.e., 2.4GHz) and high frequency (i.e., 5GHz) bands, where θ is 0 (i.e., in the Z direction, right above), and the axial ratio of the XZ plane to the YZ plane is less than 3 dB.

In summary, the antenna unit of the dual-band circularly polarized antenna structure of the present invention uses the first radiator and the second radiator as two starting points at the positions close to the feeding portion and the first grounding portion, respectively, to surround the two spiral portions outwards, and the feeding portion is coupled to the microstrip line below the antenna unit, so that the dual-band circularly polarized antenna structure of the present invention can provide a broadband dual-band. In addition, the design can ensure that the length, the width and the volume of the antenna unit do not need to be too large, so that the dual-frequency circularly polarized antenna structure has small volume.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A dual-band circularly polarized antenna structure, comprising:

an antenna unit disposed on a first substrate, the antenna unit comprising:

the first radiator is provided with a feed-in part and a first spiral part, and the starting point of the first spiral part surrounds outwards from the part close to the feed-in part; and

a second radiator, having a first grounding part and a second spiral part corresponding to the feed-in part, wherein the starting point of the second spiral part is not overlapped with the first spiral part from the part close to the first grounding part and surrounds outwards, and one of the first radiator and the second radiator is also provided with a second grounding part;

a microstrip line disposed on a second substrate spaced apart from the first substrate by a distance and disposed in parallel, the feed-in portion of the first radiator of the antenna unit being coupled to the microstrip line; and

a ground plane disposed on the second substrate, wherein the second ground portion and the first ground portion are coupled to the ground plane.

2. The dual-band circularly polarized antenna structure of claim 1, wherein the antenna unit is disposed on an upper surface of the first substrate, the microstrip line is disposed on one of an upper surface and a lower surface of the second substrate, and the ground plane is disposed on the other of the upper surface and the lower surface of the second substrate, wherein the upper surface of the second substrate is adjacent to the first substrate compared to the lower surface.

3. The dual-band circularly polarized antenna structure of claim 2, wherein the microstrip line comprises a first segment, a second segment, a third segment and a fourth segment from the center to the edge of the second substrate, the widths of the second segment and the fourth segment are greater than the widths of the first segment and the third segment, and the length of the second segment is between 3 mm and 4 mm.

4. The dual-band circularly polarized antenna structure of claim 1, wherein the first spiral portion and the second spiral portion respectively extend from the start point of the first spiral portion and the start point of the second spiral portion to a center to form two rectangles, the feeding portion and the first grounding portion are respectively located on the two rectangles, the connection direction of the two rectangles is perpendicular to the extension direction of the microstrip line, and the first radiator has the second grounding portion.

5. The dual-band circularly polarized antenna structure of claim 1, wherein the first spiral portion and the second spiral portion respectively extend from the start point of the first spiral portion and the start point of the second spiral portion to a center to form two rectangles, the feeding portion and the first grounding portion are respectively located on the two rectangles, the connecting direction of the two rectangles is parallel to the extending direction of the microstrip line, and the second radiator has the second grounding portion.

6. The dual-band circularly polarized antenna structure of claim 4 or 5, wherein the width of each rectangle is between 1.5 mm and 2.5 mm, the length of each rectangle is between 3.5 mm and 5 mm, and the distance between the two rectangles is between 1.5 mm and 2.5 mm, wherein the width of the rectangle is perpendicular to the line connecting the start point of the first spiral part and the start point of the second spiral part, and the length of the rectangle is parallel to the line connecting the start point of the first spiral part and the start point of the second spiral part.

7. The dual-band circularly polarized antenna structure of claim 1, wherein a distance between a center of the first spiral portion and the second spiral portion and the feeding portion is between 2 mm and 3 mm, a distance between the center and the first ground portion is between 2 mm and 3 mm, and a distance between the center and the second ground portion is between 6 mm and 8 mm.

8. The dual-band circularly polarized antenna structure of claim 1, wherein the distance between the beginning of the first spiral portion and the beginning of the second spiral portion is between 8.5 mm and 12.5 mm, and the diameter of each of the first spiral portion and the second spiral portion is between 50 mm and 55 mm.

9. The dual-band circularly polarized antenna structure of claim 1, wherein the feeding portion, the first grounding portion and the second grounding portion are arranged in a straight line.

10. The dual-band circularly polarized antenna structure of claim 1, wherein the first radiator has the second ground portion, the second ground portion is located at a position rotated by 260 degrees from the feeding portion along the first radiator, the second radiator further has a third ground portion coupled to the ground plane, and the third ground portion is located at a position rotated by 180 degrees from the first ground portion along the second radiator.

11. The dual-band circularly polarized antenna structure of claim 10, wherein the microstrip line has a first segment, a second segment, a third segment and a fourth segment, the widths of the second segment and the fourth segment are greater than the widths of the first segment and the third segment, the length of the second segment is between 7 mm and 9 mm, and the length of the third segment is between 2 mm and 4 mm.

12. The dual-band circularly polarized antenna structure of claim 10, wherein a connection line between the feeding portion and the first grounding portion is perpendicular to the extension direction of the microstrip line.

13. The dual-band circularly polarized antenna structure of claim 10, wherein an angle between a connection line of the feeding portion and the first grounding portion and the extending direction of the microstrip line is 10 degrees to 20 degrees.